The ever increasing demand for high bandwidth services to homes and private enterprises has prompted ongoing investigations into methods of meeting these demands. It is well known that optical fiber links can propagate the required bandwidth for providing real time services such as voice and video. Progress in the installation of fiber to each and every home has been delayed due to the extreme costs associated with providing and connecting the necessary optical cables. For this reason efforts have been extended into finding ways of making use of the ubiquitous twisted copper pair which connects virtually every home to the Public Switch Telephone Network (PSTN).
Technologies such as Asynchronous Digital Subscriber Line (ADSL) have been successful in transferring signals in the low Mbps data rate over distances of a few thousand meters. There is, however, a need to deliver higher data rates for improved multimedia services and these needs can be met by a combination of optical cable and the twisted copper pair. Programs which introduce technologies like FTTN (fiber to the neighborhood) have meant that optical fibers are connected from a central office to one or more locations within a neighborhood or apartment building and the twisted copper pair is used to connect from this termination to the customer premises equipment. This reduces the transmission distance to a few hundred meters or more. It has been established that Very High Rate Digital Subscriber Line (VDSL) technology can transmit much higher data rates albeit over a shorter distance. At present data rates in the 13 mbps to 55 mbps can be achieved using VDSL technology.
VDSL technology typically uses discrete multi-tone (DMT) and Fast Fourier Transform (FFT) technologies. In such systems the available bandwidth is used to carry multiple channels of information and a Fast Fourier Transform (FFT) is typically used to convert frequency domain modulated signals into time domain signals. In this technology a transmitter at the local Neighborhood Termination (NT) receives the data from the central office and converts it through an Inverse FFT function into a form for downloading on the twisted copper pair. At the receiver a Fast Fourier Transform function is used to obtain the original frequency signal. For large channel bandwidths with a large number of subchannels being used such as in the VDSL application, the FFT size, by necessity, is very large. This introduces two main drawbacks which make the DMT application in VDSL almost impractical. The first is tat the FFT size is very large and this impacts from a chip design perspective and the second is that the execution of the function will take a long time. Accordingly, there is a requirement to develop a system for the efficient implementation of an FFT in DMT applications.